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ANTI LOCK BRAKING SYSTEM PDF

Wednesday, July 31, 2019


Jan 4, PDF | Antilock Breaking System (ABS) is used in advanced automobiles to prevent slip and locking of wheel after brakes applied. 10/ QUICK TIPS: Anti-Lock Braking Systems (ABS). How Does ABS Work? If either of a motorcycle's tires loses traction and skids along the road surface. An anti-lock braking system (ABS) is a safety anti-skid braking system used on aircraft and on Program Task 4: A Test Track Study of Light Vehicle ABS Performance Over a Broad Range of Surfaces and Maneuvers, Jan " (PDF).


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towards the car that turned in front of you. Had your car been equipped with an anti-lock braking system. (ABS), your wheels would not have locked up, and. This is achieved by the use of ABS. (Anti-Lock Braking System), which prevent the road wheels locking up wheels locking up p. g p. (by sensing a locked wheel, . Oct 4, Antilock Breaking System (ABS) is used in advanced automobiles to prevent slip and locking of wheel after brakes applied. It is automobile.

In fact, this situation occurs, when either the desired slip s, has been chosen on the instable side of the friction characteristic, or when a sudden change in ground force is encountered e.

The principle problem in ABS design is that the optimum slip and the exact shape of the adhesion characteristic depend on the runway surface and further parameters, which cannot be measured, such as the condition of the tyres or the dynamics of the normal forces. If it is too small the braking force might become insufficient, if it is too high, wheel lockup occurs. Recently there has been a growing interest in intelligent control techniques for the design of aircraft and road vehicle Antilock Brake Systems ABS.

In particular, rule-based, fuzzy logic controllers have been applied to this problem and successfully tested in simulation. In fact, the use of non-linear, fuzzy control techniques appears to be particularly appropriate for the ABS control problem because of the high non-linearity of the system and the lack of a precise physical model of the friction force between tyre and runway.

In addition to that, the controller must operate at an unstable equilibrium point to achieve an optimal braking performance. The most important problem in ABS control design - fuzzy or conventional - is that the optimum adhesion coefficient varies significantly with the surface condition i. Because the latter is unknown, it is extremely difficult to define a controller that guaranties an optimal braking performance for all types of runway conditions.

A typical ABS includes a central electronic control unit ECU , four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel.

The wheel then turns faster. Conversely, if the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel. This process is repeated continuously and can be detected by the driver via brake pedal pulsation. This system receives information from the sensors and then effects the hydraulics of the brakes. When a rapid lock is detected, the anti-lock system reduces the hydraulic pressure in the brake cylinders, releasing the brakes and preventing the wheels from locking.

The master cylinder controls the hydraulic pressure in the brake cylinder. The hydraulic system connects to the master cylinder with brake cylinder. The hydraulic fluid must pass through a chamber to reach master cylinder and brake cylinder.

When the brakes are in normal use, the valve is open and the pressure in the reservoir is the same as the pressure in the main cylinder and in this case the anti-lock braking system does not work since there is no rapid braking. When the sensor detects sudden braking, the control valve moves.

The control valve determines the pressure in the gap in front of the actuator. Larger pressure in the chamber upstream of the actuator causes back slip and closes the valve between the master cylinder and chamber. As the actuator slides backwards, the volume of fluid in the reservoir increases. This reduces the pressure of the hydraulic fluid and releases the brakes which prevent locking.

Figure 3. Main Components of ABS 4. Hydraulic Control Unit The hydraulic unit adjusts the brake cylinder pressure of each wheel with commands coming from the engine control unit ECU. During this adjustment, solenoid valves are used.

Where the car's engine is located, the main brake is positioned between the master cylinder and the wheel brake cylinders. Thus, the connections to the brake center cylinders and the links to the wheel brake cylinders are kept short. The hydraulic units have inlet and outlet solenoid valves for controlling each wheel pressure.

The ECU plays an important role in this part and fulfills all electronic and electrical tasks with the control functions of the system. Figure 4. Wheel Speed Sensor The ECU, or engine control unit, uses the signals from the wheel speed sensors to calculate the speed of the car's wheels. There are two principles in this regard, active and passive wheel speeds.

Whether active or inactive, both speeds measure the speed of the wheels with the magnetic field, without touching the wheels. Today more active sensors are used.

Active sensor variants can control both the direction of rotation of the wheels and the speed of the wheels. Figure 2. Deceleration Sensor During braking on four-wheel-drive vehicles, it detects the vehicle's deceleration rate and sends these signals to the ECU. The ECU uses these signals to determine precisely the road surface conditions and make the required control measurements. The deceleration speed sensor is located in the luggage compartment in passenger cars and in the engine compartment in other vehicles.

Deceleration sensor contains two pairs of LEDs light emitting diode and one channel with photo transistor plate and a signal conversion circuit. When the vehicle's deceleration rate changes, the channel plate is rocked along the longitudinal direction of the vehicle in accordance with the deceleration rate.

Channels on the channel plate open and close the photo transistor by cutting off the light coming from the photo-transistor from the LEDs.

The rate at which these transistors turn on and off is divided into four levels, which are signaled to the ECU. Valves The Hydraulic Control Unit controls these valves which are continuously active in the system. The main tasks of valves are; In the first position, valve open; the pistons in the caliper are braked by giving full power to them. In the second position cuts the valve line; it cuts off the hydraulic flow on the line leading to the piston and no power is transmitted even when the pedal is pressed.

Hydraulic Pump When the flow of the valve line is stopped, the hydraulic pressure is released from the pump to regain the lost pressure. This process is repeated every time when the hydraulic pressure decreased due to opening of valves.

It is located on the hydraulic unit. ABS Control Module ABS Control Module is a microprocessor that evaluates the information transmitted by the wheel speed sensors and with this information it controls the ABS system by giving the necessary commands to the actuators.

Generally, it is located under the hydraulic unit. In some vehicles the hydraulic unit may have been mounted at a different location. In the event of a fault, the ABS and the connected systems are disabled, some failures may cause problems with other systems, and the ABS warning lamp is turn on. Types of ABS 5. On vehicles with ABS on all four wheels, the braking systems of the cars prevent the wheels from locking on all four wheels.

The driver can control the vehicle better and it is easier to keep the vehicle under control. At this time, the braking pressure required for braking is set. If only the rear two wheels have ABS; this situation is usually found in trucks, minibuses and sports cars. The car is prevented from locking only on the rear wheels.

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In this case, the driver must manually adjust the pressure on the brake pedal. Thus, the driver can conveniently orient the car in the desired direction and provide safe driving. Figure 5. Each wheel is controlled independently.

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Steering safety and stopping distance on all road conditions are protected. In front-wheel drive vehicles, most of the weight is on the front wheels due to engine and transmission system located in front of the vehicle.

The yawing moment that causes the speed difference on the wheels on the rear axle on different road 15 Department of Mechanical Engineering, Eastern Mediterranean University surfaces can cause the vehicle to be out of balance. For this reason, vehicles with four- channel ABS have a low-logic choice on the rear wheels to maintain the balance of the vehicle in the majority.

Three-channel Three-sensor ABS The three speed sensors measure the number of revolutions of both the wheel and differential sun gear.

The braking force on the front wheel is adjusted separately by solenoid valves. The braking force of the rear wheels is regulated by a single solenoid valve.

This type hydraulic units are used in parallel brake circuits. Two-channel ABS This type of hydraulic unit is used on heavy vehicles or on vehicles such as trucks.

Only the rear two wheels are controlled. The ABS commands the brake pressure as a function of the difference between the measured and the reference wheel speed.

The latter is calculated from the measured aircraft speed and the desired wheel slips, using equation. At the moment, when the pilot pushes the brake pedal the brake pressure and the wheel slip increase provoking a ground force between tyre and runway.

Assuming the case of full braking, the ABS will control the wheel speed to its reference value. To achieve a maximum braking force the reference slip should be chosen close to the optimum slip. The slope of u s being negative, the wheel immediately starts to lock. In this case, the ABS rapidly releases the brake pressure to force the wheel speed back to the stable side of the adhesion curve.

Anti-lock braking system

In fact, this situation occurs, when either the desired slip s, has been chosen on the instable side of the friction characteristic, or when a sudden change in ground force is encountered e. The principle problem in ABS design is that the optimum slip and the exact shape of the adhesion characteristic depend on the runway surface and further parameters, which cannot be measured, such as the condition of the tyres or the dynamics of the normal forces. If it is too small the braking force might become insufficient, if it is too high, wheel lockup occurs.

Recently there has been a growing interest in intelligent control techniques for the design of aircraft and road vehicle Antilock Brake Systems ABS.

Anti-Lock Braking System (ABS) (All)

In particular, rule-based, fuzzy logic controllers have been applied to this problem and successfully tested in simulation. In fact, the use of non-linear, fuzzy control techniques appears to be particularly appropriate for the ABS control problem because of the high non-linearity of the system and the lack of a precise physical model of the friction force between tyre and runway.

In addition to that, the controller must operate at an unstable equilibrium point to achieve an optimal braking performance.Some systems are equipped with a rear wheel lift off mitigation functionality.

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It provides traction even on low friction surfaces. Wheel moment of inertia, Rotational wheel speed, Friction coefficient, Wheel Radius Normal force per wheel Friction force, Aircraft speed Figure 1b: are analogous to the above vehicle wheel shown.

Anti-lock Braking System (ABS): Advantages and Disadvantages

Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock. When pressure should be released, a linear motor pulls back the plunger piston and opens up more space for the fluid.

The distinctive feature of the system is that there is no independent speed sensor for each wheel.

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